Several hundred people targeted players such as Nigel de Jong and Gregory van der Wiel when 25,000 spectators attended the Dutch practice session at the Stadion Miejski, the home of Wisla Krakow.

The players, on the instructions of the captain, Mark van Bommel, responded by moving their training drills to the other side of the ground. "It is a real disgrace especially after getting back from Auschwitz [the Dutch squad had visited the concentration camp on Wednesday] that you are confronted with this," Van Bommel said. "We will take it up with Uefa and if it happens at a match we will talk to the referee and ask him to take us off the field."

The problems occurred as the players began the session by jogging a lap of the pitch only to be greeted at one end of the stadium with monkey noises and loud jeers. On the second circuit, they were even louder and it was then the players decided not to go around again. "At least now we know what we can encounter," the Holland coach, Bert van Marwijk, said with heavy cynicism. "Very atmospheric."

Uefa subsequently tried to deny that it was racially motivated, saying they had checked with the Dutch squad and had been told it was not thought to be of that nature. Instead, the official line is that a small part of the crowd was protesting about the fact that Krakow had not been made one of the host cities. Another theory that has been put forward is that Wisla's supporters did not want their stadium being used by anyone but their own club and were simply booing the Dutch players.

Van Bommel, however, responded angrily when it was put to him not everyone had heard monkey noises. "You need to open your ears," he said. "If you did hear it, and don't want to hear it, that is even worse."

Privately, the midfielder is understood to be unhappy that the authorities are not treating the issue more seriously, but the incident is still threatening to be a major embarrassment for Uefa, coming before a ball has even been kicked, and will increase the scrutiny on Poland's supporters when the tournament opens with the co-hosts playing Greece in Warsaw on Friday.

The Polish authorities have been eager to dispel the sense that the backdrop to this tournament will have racism at its centre, and the country's prime minister, Donald Tusk, went through an elaborate public relations exercise on Thursday to drive home the point. Tusk was accompanied by a television crew on a 90-mile journey to Lodz to dine with Poland's first black parliamentarian, John Godson, and his family, including relatives who had flown in from Nigeria. The idea was to show the improvements both in Poland's road network and acceptance of different races.

Godson criticised the BBC Panorama documentary Euro 2012: Stadiums of Hate that had warned racism would be rife. He argued that Poland was a "hospitable and tolerant country" while Tusk wore a badge that said "Welcome" and said he was convinced there would be no problems: "I very warmly invite all English people. You will definitely not encounter anything unpleasant here."

Panorama had focused on the racist elements in the support of Krakow's two major clubs, Wisla and Cracovia, as well as highlighting the seriousness of the problem in Ukraine. Michel Platini, the Uefa president, has subsequently said the referees have been empowered to take teams off the pitch if there are serious issues – but added that any player who walked off without permission would be booked.

The families of two of England's black players, Alex Oxlade-Chamberlain and Theo Walcott, have already decided against travelling to the tournament because of the potential problems. England are based in Krakow, along with the Netherlands and Italy squads, and will allow the public to watch Friday's practice session at Hutnik stadium on the outskirts of the city.